The chemical and physical mechanisms with which emulsions of oil and water are formed are well-known. The knowledge accumulated suggests that when water is broken into relatively small-size drops and dispersed through oil, the drops are surrounded with a film of a material which is strongly hydrophilic. This film of emulsifier effectively isolates the droplets of water from each other. When the isolating film is effective, the emulsion is classified as stable, the water droplets remaining dispersed through the oil. Therefore, to de-emulsify, a force is needed to penetrate, or weaken, the hydrophilic film of emulsifier which surrounds each water droplet so that the droplets of water can then be driven together in coalescense. A strongly lipophilic material is needed to exchange, neutralize, or disrupt the electrical charges within the hydrophilic film and thereby penetrate, or weaken, the film.
The mechanism by which a de-emulsifier weakens, or penetrates, the film of hydrophilic emulsifiers is controversial to some extent. There is investigation that suggests the exchange of electrical charge between the hydrophilic emulsifier film about the water droplets and de-emulsifying material. The precise nature of this interaction between emulsifying and de-emulsifying materials need not be developed at this time. It is sufficient to describe the emulsifying material as hydrophilic and the de-emulsifying material as lipophilic. A responsible statement is that some type of electrical exchange takes place to weaken, or penetrate, the hydrophilic film with resulting coalescence of the water droplets.
The days when empirical methods stumbled upon effective de-emulsifying compounds is long past. Backed by some accumulated knowledge of the mechanisms of emulsification and de-emulsification, compounds are now being systematically developed which apply obviously effective force to neutralize the various emulsifying agents which exist in water-in-oil emulsions.
One popular methodology of characterizing the de-emulsifying material is to categorize the de-emulsifying agent with respect to its relative solubility in water and in oil. Four such categories then depict the interactions which specify the nature of the de-emulsifying agent: lipophilic-hydrophobic (LIHO), lipophilic-hydrophilic (LIHI), lipophobic-hydrophobic (LOHO), and lipophobic-hydrophilic (LOHI). (Lipo- meaning oil, hydro- meaning water, -philic meaning loving, and -phobic meaning hating). The type of interaction (solubility) of the de-emulsifying material required to dehydrate oil effectively is highly dependent upon the nature and quantity of the stabilizing emulsifier. As each interaction suggests, the de-emulsifying material contains chemical functionability which renders the de-emulsifying agent interface active; the de-emulsifying agent is attracted to and may concentrate at the oil-water interface of an emulsion. For ease of application, it has been common practice to develop de-emulsifying materials which primarily exhibit LIHO or LIHI characteristics; oil loving--water hating, or oil loving--water loving characteristics.
There is another school of thought which emphasizes that the most important characteristic of the de-emulsifying material is its wetting characteristics, while another school teaches that the de-emulsifying agent must be interface active, but neither appreciably soluble in the oil or water. It must be remembered that the importance of the de-emulsifying material in resolving emulsions is not bound to theoretical considerations of its solubility, wetting, or interfacial activity, but bound to performance.
One popular, and well-known, de-emulsifier compound is the polyester. When a polyol is brought together with a polybasic acid under the proper reaction conditions in the presence of an appropriate catalyst, the --OH of the polyol will combine with the --COOH of the polybasic acid to form water and a polyester. The resulting polyester is a de-emulsifier. The present problem is how to strengthen this de-emulsifier.